Microdialysis is a method of examination in which a probe is inserted into tissue in vivo, such that one side of a semi-permeable membrane is in contact with tissue and extra cellular liquid and the other side is flushed or rinsed with a dialysis liquid (perfusate) which takes-up substances from the extra cellular liquid through the membrane. These substances can then be analyzed in the dialysate on or after exiting the probe.
Microdialysis probes are by nature fragile and very small, which requires great care in inserting and withdrawing the probe from the tissue in which it is used. However, it is also of great importance that the probe when inserted into tissue of a living person, is placed in the intended location such that when measuring the probe actually through microdialysis measures the intended chemical/biological variables that at each measurement is of interest. It is of course important in these measurements to know exactly what is measured.
The use of microdialysis becoming more frequent and common raises other problems such as monitoring and control of the probe during insertion and use. It is a fact that microdialysis provides a unique possibility to examine the equilibrias of substances and/or the amounts present or missing of substances or to monitor specific changes in the status of substances connected with e.g. the use of medicaments, in surgery etc.
The monitoring and control of the probe position during insertion/withdrawal and use-has been an obstacle in so far that the smallness and the material of the probe does not make possible the use of common methods for detecting the probe once the insertion has been started. This becomes more problematic the deeper into the tissue the microdialysis is to take place.